Corrosion of pipelines is a major concern for the oil industry. Over the past two decades, it has become clear that corrosion in water injection pipelines is to a large extent caused by H2S-producing bacteria; this phenomenon is commonly referred to as microbially-induced corrosion (MIC). The bacteria responsible for corrosion belong to a group of sulphate-reducing bacteria (SRB), which are active under anaerobic conditions.
SRB's can be found in almost all natural environments such as soils, fresh and marine waters, hot springs, geothermal areas, oil and gas wells, and in sewage systems. In addition to induced corrosion of surface facilities, production of H2S causes reservoir souring requiring additional safety precautions at the production side. The bacteria are sessile (they grow on surfaces) and protect themselves by forming biofilms, which cause bio-fouling if not properly removed.
In the oil industry, commercial biocides such as formaldehyde, glutaraldehyde or tetrakishydroxymethyl phosphonium sulphate (THPS) are or have been used in water injection pipelines to inhibit growth of microorganisms. These chemicals are typically expensive, can be dangerous to handle, may have a negative impact on the environment and are only partially efficient in controlling bacterial growth in biofilms.
Treatment of drinking water with ultraviolet (UV) light is a method, which has been in use since 1955. The bacteria will absorb UV light within a certain range of wavelengths, which will cause their DNA to undergo physical changes preventing further cell replication. The water has to be clear without any suspended solids for this mechanism to have any effect. Furthermore, this technology has not been deployed on a continuous basis.
Other methods include removal of sulphate from the injected seawater to deprive the SRB from their nutrient.
Another way to combat H2S production is to add nitrate to the injected seawater to stimulate a competing group of nitrate-reducing bacteria in the reservoir that produce nitrite. Nitrite will then inhibit SRB functionality leading to reduced production of H2S. One problem of this solution is that other nitrite-reducing bacteria can counteract this inhibition by reducing nitrite to ammonia resulting in minimized nitrite-induced inhibition of SRBs.
U.S. Pat. No. 7,169,618 describes separation of cells from a medium using magnetic particles comprising a coupling molecule to capture the cell. The coupling molecule may be one of the members of a specific binding pair, e.g. antigen/antibody; enzyme/substrate; metal ion/chelate and so forth. The separation described in U.S. Pat. No. 7,169,618 is useful for analytical, preparative diagnostic or therapeutic techniques.
Inhibiting the growth of bacteria, particularly SRB's and other H2S-producing bacteria remains a matter of importance for the oil industry and is of significant financial importance to the oil and related industries.